Abstract: Vasculopathy associated with Sickle Cell Disease (SCD) is multifactorial and the pathogenesis remains incompletely understood. To date, both clinical and experimental evidence concludes that reduced NO bioavailability and/or responsiveness is a contributing factor to vasculopathy in SCD. This proposal aims to elucidate a novel reduction-oxidation (redox) regulation mechanism ? the CyB5R3-depenent reduction of sGC- that controls NO sensitivity in vascular smooth muscle cells (VSMCs) and its impact on vasculopathy and in SCD. Importantly, by using a bench-to-bedside approach, we characterize this signaling pathway with gain and loss of function in cell culture. We explore the impact of this signaling pathway on the development of vasculopathy in the humanized transgenic sickle cell mouse (BERK) and chimeras transplanted into a tamoxifen-inducible Cre-Lox smooth muscle specific CyB5R3 knock-out. Finally we will extend these insights to the bedside by characterizing the effect of loss of function CyB5R3 T117S polymorphic variants on endothelial function. We test a personalized or precision medicine approach to improve the health of individuals with SCD with PH, via the targeting of new sGC modulator drugs to responsive Cyb5R3 genotypes. Considering the defining role of sGC in NO signaling and the fact that the oxidation state of sGC may predict responses to new classes of sGC activator and stimulator medications, we anticipate that these studies will significantly impact our understanding of biology, precision therapeutics (right drug for the right patient) and pharmacogenetics (polymorphism based drug selection).